Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the annotations, the description discloses the payment-gated behavior, the exact no-payment branch returning a PaymentRequired/isError document, asynchronous settlement, and the final orderKey result. This gives the agent a clear model of the tool's side effects for an open-world, paid operation.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three sentences with no wasted words. The purpose and payment mechanism are front-loaded, and the error and success paths are presented in a clean if-then structure.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a tool with no output schema, the description covers the key outcomes, PaymentRequired vs orderKey, and points to the next tool in the workflow. It does not state the exact price/amount or enumerate all error cases, but the core invocation and settlement flow are sufficiently complete.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The schema already documents targetAddress and language at 100%, so the baseline is satisfied. The description adds crucial invocation context by naming the _meta['x402/payment'] field and explaining the PaymentPayload requirement, which is not visible in the input schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with 'Paid over x402 in USDC on Base', identifying the action (buy), the artifact (Flash Report), and the payment channel. It also separates buying from collecting by returning an orderKey to use with collect_flash_audit, making the purpose unambiguous.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives clear operational context: payment is required, absence of payment yields a PaymentRequired response, valid payment leads to async settlement and an orderKey, and wallet-less users are routed to the web store. It does not explicitly differentiate from siblings like buy_contract_data or check_contract_free, so it lacks a fully explicit when-not-to-use statement.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.